1. Field of the Invention
This invention relates to a device for feeding sheet-like image-bearing members (hereinafter simply referred to as sheets) cut into a predetermined size and used with copying machines, recording apparatuses, printing machines and the like. More particularly, it relates to improvements in a sheet feeding device having a feed roller for feeding one by one sheets piled on a paper feed bed or in a cassette or the like, said roller having a cross-section in which part of the circumference thereof is cut away so that, during the non-feeding, the uppermost surface of the piled sheets and said roller maintain a non-contact condition with the aid of said cut-away part.
2. Description of the Prior Art
FIG. 1 of the accompanying drawings shows a cross-section of the conventional feeding device having such sheets contained in a cassette. This feeding device is of a well-known construction and the sheets 2 contained in the cassette 1 lie on a support plate 5 having one end pivotally supported by a pivot pin 3 and the other end biased upwardly by a coil spring 4. At the corner portions of one end of the sheets 2, separation and keep pawls 6 control the height of the sheets. On the other hand, a feed roller 7 is of a known construction having a cross-section in which part of the circumference thereof is cut away. More particularly, the feed roller comprises a mandrel 9 secured to a square bar 8 which provides a rotary shaft rotatable in the direction of the arrow, and a rubber member 10 which is a material of high friction coefficient is adhesively secured to the portion of the roller which acts as the actual roller. Designated by 11 adjacent to the roller 7 is a guide plate for the sheets 2 being conveyed. A sheet 2 may be guided by the guide plate 11 toward a set of register rollers 12. The mandrel 9 and the rubber member 10 may be integrally formed of rubber or like material.
In the above-described construction, the actual paper feeding operation may be effected by the square bar 8 making one full rotation in the direction of the arrow with the aid of a one-rotation clutch (not shown) operated by a paper feed signal. At this time, the length of the arc of the rubber member 10 may be sufficient to cause a predetermined amount of loop to be formed by a fed sheet 2 bearing against the inoperative register rollers 12 from the moment when the member 10 contacts the sheet 2 to feed the sheet from the cassette 1. The sheet forming the loop may be conveyed to a subsequent process portion by the register rollers 12 which will soon begin to be rotated in synchronism with the rotation of a photosensitive medium or the like. The loop of the sheet is necessary for preventing oblique movement of the sheet 2 which may be created by the roller 7.
In the feeding of the above described construction, it is unnecessary to lower the cassette or to raise the roller 7 when the cassette 1 is replaced by a new one because the roller 7 and the sheets 2 are in non-contact state (state of FIG. 1 during the non-feeding. This also leads to the same effect with respect to a paper feeding bed which does not use a cassette. Further, the sheet feeding of the above-described construction may be accomplished by the roller 7 being simply rotated while being fixed, and this leads to simplification of the drive system and mechanism. However, the feeding device of FIG. 1 suffers from problems which will hereinafter be described in conjunction with the accompanying drawings.
FIG. 2 shows a cross-section of the feeding device when only a few sheets 2 are left on the support plate 5. When compared with the state of FIG. 1, it will be seen that the support plate 5 has pivoted about the pin 3 so that the inclination of the sheet surface at the forward end of the sheets has been greatly varied. The amount of such variation in inclination is specifically shown in FIG. 3.
In FIG. 3, line 13 indicates the locus of the outer circumference of the rubber member 10 when the roller 7 is rotated. Line 2aindicates the sheet surface position when the sheets 2 are supported to a maximum limit (hereinafter referred to as the condition 1), and line 2bindicates the sheet surface position when only one sheet is left (hereinafter referred to as the condition 2). In such a construction wherein the support plate pivots about a predetermined point in accordance with the number of sheets, the inclination of the sheet surface is varied in accordance with the number of sheets supported on the support plate. As is apparent from FIG. 3, the point at which the rubber member 10 contacts the sheet 2 moves from a point A to a point B. That is, the feeding is started earlier in the condition 1 by an amount represented by AB in the condition 2. The time point whereat the feeding is started affects the amount of the loop later formed by the sheet: if the amount of loop is set to an optimal value during the condition 1, the amount of loop will be insufficient during the condition 2, and if the amount of loop is set to an optimal value during the condition 2, the amount of loop will become too great during the condition 1.
The amount of loop, even if increased to some extent, may sometimes be absorbed where the distance between the feed roller 7 and the register rollers 12 is long or where the space defined by the guide plate 11 is sufficiently wide. However, if the apparatus is a small one such as a compact copying machine, application of the above-mentioned countermeasure is difficult and too great a loop may sometimes cause oblique movement or wrinkling of sheets or jam of the sheets.